Over one billion silicon-based image sensors were produced worldwide in 2013. Typically, imaging sensors use p-n or p-i-n junctions to separate and collect photo-excited electron-hole pairs. For low-light situations and high-density pixels, a single photodiode may produce small amounts of photocurrent, limited by the quantum efficiency of light absorption and requiring extremely low-noise electronics to amplify the signal.
Typically, imaging sensors may use pn or p-i-n photodiodes as photodetectors and perform color selection with dielectric or organic dye color filters. For low light or high pixel density sensors, photodiodes may require ultralow-noise amplifiers since they do not exhibit photocurrent gain. Dielectric filters are typically fabricated off-chip, limiting their use with small pixels; organic dye filters degrade under exposure to ultraviolet light, limiting their durability.